Recent advances in genetic and molecular technologies are providing the basis for a dramatic increase in our understanding of how the genetic repetoire of organisms establishes the basic embryological plan. Saturation screens for female sterile, zygotic lethals, and vital genes which have a critical role in oogenesis are being carried out to provide the tools for a molecular understanding of the events of early development. Recent discoveries of the "homebox" sequence in Drosophila and its homologues in human DNA have increased the significance of the use of model organisms. In addition, the basic developmental plan of organisms lays the foundation for future normal patterns of growth and development. In this project detailed genetic and molecular analysis will be undertaken to understand the sets of loci responsible for establishing the developmental potential for the posterior region of the Drosophila egg. Libraries of genes specifically active in the pole cells (primordial germ cells) will be constructed and genes whose products are localized to the ooplasmic germ plasm will be studied. In addition, two sets of maternal effect loci hae been identified which are essential for the proper determination of the posterior 20% of the egg. One set eliminates not only the germ plasm but also disrupts the abdominal field except for the terminalia and posterior endodermal derivatives; the second affects the reciprocal set of posterior structures, that is, the germ plasm and anterior abdomen are present but the abdominal terminalia and posterior endoderm are completely missing. Both detailed developmental and molecular analyses of specific examples of each of these classes of mutations will be studied. The long term goal is to provide the genetic and molecular basis for understnding the genetic control of posterior egg structure and function.